1. Field of the Invention
The present invention pertains to a precision gas flow meter, and more particularly to a gas flow meter that measures volume incrementally.
2. Description of Related Art
There are several methods for measuring the volumetric flow rate of a gas. Indirect measurement methods include pressure drop across an orifice, (bobbin rotameter) mechanical movement (rotating a blade or moving a sail switch), heat transfer, (hot wire anemometer) or ultrasound interference. Each of these methods require measurement or knowledge of the gas composition and work best with a steady state gas flow. These methods are not precise for intermittent flow or low flow rates below a predetermined range. Positive displacement methods include liquid displacement spirometers, diaphragm activated devices and rotary vanes. These mechanical systems also perform best at a fairly constant flow rate and require a predetermined pressure difference to function.
These aforementioned devices do not lend themselves to precision measurements of very small volumes of gas flow (less than 0.1 liters per minute) due to seal leakage, required operational pressure drop and difficulty in precise calibration of these mechanical devices Some of these methods such as the spirometer or bobbin rotameter cannot be used to measure reversible gas flow.
Precision measurement of gas flow in small volume increments is required in many processes including biological reactors, chemical reactors and thermal-chemical reactors. Measurement of intermittent or reversible flows is also required.
What is needed is a method and apparatus to conduct precision measurement of small quantities of gas flow. The ability to measure intermittent and reversible gas flow is also needed.